1. Field of the Invention
The present invention relates to a wireless communication system, especially to a device and method for transmitting control channel with pre-allocated resources in the wireless communication system.
2. Description of the Related Art
At present, the 3rd Generation Mobile Communication System Partnership Project (referred to as 3GPP) standardization organization has commenced on Long-term Evolution (referred to as LTE) to an existing system criteria. Among numerous physical layer transmission techniques, both a downlink transmission technique based on OFDM (Orthogonal Frequency Division Multiplexing) and an uplink transmission technique based on SCFDMA (Single Carrier Frequency Division Multiple Addressing) are the main premises for present standardization. In nature, OFDM is a multi-carrier modulation communication technique. Its basic principle is to divide a high rate data stream into multiple low rate data streams to be transmitted via a group of orthogonal sub-carriers simultaneously.
Due to the nature of multi-carrier, the technique of OFDM bears some technical advantages in reducing the complexity of an equalizer in a receiver and reducing an ISI (inter-symbol interference) through the introduction of CP (cyclic prefix) and so on. SCFDMA is essentially a single carrier transmission technique. With it, a PAPR (Peak to Average Power Ratio) is comparatively lower in a transmitter. Therefore, a power amplifier of a mobile terminal can be operated effectively to enlarge the cell coverage. In addition, good performance of comparatively lower processing complexity is held in the receiver.
Main principle concepts on LTE are illustrated in FIG. 1, FIG. 2 and FIG. 3.
According to existing discussions on LTE, the frame structure of the downlink in an LTE system is illustrated in FIG. 1. In an LTE system, the radio physical resource refers to time and frequency resources that a system or a user can occupy. It can be described with the radio frame (101-103), which bears the same time length as that in a WCDMA (Wide Band Code Division Multiple Access) system, i.e., 10 ms. Each frame is divided into several slots (104,105,. . . ,107). At present, it is supposed that each radio frame includes twenty slots of 0.5 ms. Each sub-frame includes multiple OFDM symbols. There are two types of time lengths of OFDM symbol's CP, i.e., the shorter CP's time length is about 4.8 μs and the longer CP's time length is about 16.7 μs. The longer CP slot is used for multi-cell broadcast/multicast and in the case that the cell is very large and the shorter CP slot is used for Unicast and in the case that the cell is very small. The shorter CP slot (108-114) includes seven OFDM symbols, and the longer CP slot (115-120) includes six OFDM symbols. According to present discussion, the TTI (transmission time interval) is specified as 1 ms, i.e., the time length of two slots (2×0.5 ms).
According to present assumptions for LTE research, FIG. 2 illustrates an uplink frame structure in an LTE system. Similar to the downlink frame structure, the time length of a radio frame (201, 202, 203) is the same as that in a WCDMA system, i.e., 10 ms. Each frame is divided into several slots (204, 205, 206, . . . , 207). Each radio frame includes twenty slots of 0.5 ms and each slot includes seven SCFDMA symbols (208-214). According to present discussion, transmission time interval (TTI) is 1 ms, which equals the time length of two slots.
FIG. 3 illustrates a processing process of SCFDMA signal. After some certain processing, a sending end gets modulation symbols (301) needed to be transmitted. The symbol is transformed to frequency domain through a DFT module (302), mapped to a sub-carrier position allocated through a sub-carrier mapping module (303), and then transformed to time domain through an IFFT module (304). After that the CP (305) is added, and the following operations are carried out. In order to distinguish with IFFT operation (304) and DFT operation carried out in the reception end, the DFT operation of module (302) is called as Pre-DFT operation.
According to present discussion progress in LTE, the physical time frequency resources of fundamental data for data transmission is divided into several radio blocks (RB) with each containing M continuous sub-carriers in frequency domain and N continuous data symbols in time domain. In the downlink, the data symbols are OFDM symbols, while in the uplink, they are SCFDMA ones. That is to say, a fundamental data physical RB consists of M*N basic time frequency resources. According to present discussion on LTE, M is specified as 12 and N is specified as the number of OFDM symbols in one slot in the downlink or the number of SCFDMA symbols in one slot in the uplink.
At present, it is considered by LTE to specify the fundamental physical RB for the transmission of control information. The used specification is just similar to that in the fundamental data physical RB, except that M or N may have different values. In present invention, for the convenience of description, the discussion is focused on the fundamental control physical RB.
Now, a basic idea on the design of LTE control channel is described so as to explain how to explicitly or implicitly indicate the physical resource used by an ACK/NACK channel.
In present research of downlink L1/L2 (L1/L2: Layer 1/Layer 2) control channel in LTE, TDM (time division multiplex) is applied in both the downlink L1/L2 control channel and the downlink data channel. The control channel is transmitted through the first n (n≦3) OFDM symbols in each TTI. Here, the L1/L2 control channel includes: a) a downlink scheduling control channel for the allocation of downlink resource; b) an uplink scheduling control channel for the allocation of uplink resource; and c) an ACK/NACK channel for acknowledgement to uplink data. At least two types of transmission formats are applied to configure each specific control channel, i.e., to configure different MCS (modulation and coding scheme). With different MCSs applied in the user equipments under different channel conditions, the efficiency of utilization can be improved in the physical layer.
MCS is a two-element pair containing a modulation scheme and an actual code rate. The modulation scheme can be QPSK, 16 QAM and so on. Given the modulation scheme, the lower the code rate is, the more protection is obtained to information bits, and given the code rate, the more protection is obtained to information bits with lower-level modulation scheme. To achieve the same link performance, UEs in good channel conditions can use comparatively higher code rate for data transmission while those in poor channel conditions should adopt comparatively lower code rate for data transmission. Values for MCS can be configured dynamically, statically or semi-statically by the system.
Present discussion in LTE to the uplink control signaling involves in the discussion to a Data Associated Signaling and a Non Data Associated Signaling. Data Associated Signaling consists of HARQ information and Transmission Format (TF) information. Non Data Associated Signaling consists of uplink Scheduling Request (SR) information; uplink ACK/NACK information, which is an acknowledgement to whether the downlink transmission data is correctly received by the uplink; and CQI (channel quality indication) information, which indicates the quality of the downlink physical channel. If there is no uplink data, the uplink control signaling is transmitted through the pre-configured frequency. As shown in FIG. 4, the pre-configured frequency areas are distributed in the two ends of the frequency band. In addition, to make use of the frequency diversity effect, a UE's uplink control signaling is transmitted through two slots in the ends of the frequency band in a TTI, i.e., through the first slot (401) in the upper of the frequency band and the second slot (402) in the lower of the frequency band, or through the first slot (403) in the lower of the frequency band and the second slot (404) in the upper of the frequency band. In the case that some uplink data is in transmission, UE's uplink control signaling is transmitted through the uplink data channel resource allocated by eNodeB, and shares the TDM multiplexing scheme with the uplink data. In this way, UE's uplink control information is multiplexed together with the UE's uplink data before the process of Pre-DFT so as to obtain single-carrier property for the uplink signal.
In an LTE system, the technique of HARQ is applied as a very important physical layer transmission technique for data transmission. To implement HARQ, the receiver feeds back ACK (data is received correctly)/NACK (error in data receiving) information according to whether the data packet is received correctly or not. During the HARQ transmission of uplink data, it is necessary for eNodeB to transmit the downlink ACK/NACK information in response to the uplink data's transmission (hereinafter referred to as downlink ACK/NACK transmission). During the HARQ transmission for downlink data, it is necessary for UE to transmit the uplink ACK/NACK information in response to the downlink data's transmission (hereinafter referred to as uplink ACK/NACK transmission).
According to present discussion progress in LTE, either a FDM (Frequency Division Multiplexing) scheme or a hybrid FDM/CDM (Frequency Division Multiplexing/Code Division Multiplexing) scheme can be applied by the UE in the downlink ACK/NACK channel. Here, FDM means that different UEs occupy different time frequency resources for ACK/NACK transmission. When ACK/NACK information is collectively transmitted through one OFDM symbol, the general FDM multiplexing scheme is shared by different UEs. While the ACK/NACK information is transmitted by distributing to several OFDM symbols, the hybrid FDM/TDM (time division multiplex) multiplexing scheme is actually shared by different UEs. For the convenience of description, the two multiplexing schemes are called FDM. FDM/CDM scheme means that different UEs share the hybrid multiplexing scheme of FDM and CDM in ACK/NACK channel, i.e., the physical resource (for ACK/NACK channel) is divided into several (greater than 2) parts in time and frequency domain, and the ACK/NACK information of different UEs is transmitted through each part of the physical resource by means of CDM multiplexing scheme.
According to discussion on ACK/NACK channel in LTE, the methods indicating which ACK/NACK channel is allocated to specific UE include an explicit indication method and an implicit indication method. These methods may be used for either the transmission of the uplink ACK/NACK information or the downlink ACK/NACK information.
In the explicit indication methods, a method is used to configure the dedicated channel for the transmission of ACK/NACK information, and transmit a UE's identifier and the corresponding ACK/NACK information. Since the UE's identifier is comparatively longer (e.g., 16 bit long) and ACK/NACK information is only one bit in general, this method is not economical in resource utilization so that it is not generally in service. Another explicit indication method means that an index allocated to a certain UE's ACK/NACK channel is contained in the control signaling which is used by eNodeB to allocate resource to the UE. Suppose that the total number of ACK/NACK channels in the system is N, it is necessary for the control signaling to contain log2(N) (ceiling integer value) bits for the index of UEs' ACK/NACK channels allocated to UE.
In the implicit indication methods, a method is to define a one-to-one mapping relation between an index of the control signaling (which is used to allocate data resource for UE) and an index of ACK/NACK channel corresponding to the allocated data resource. For instance, suppose that the index of the control channel (allocated by eNodeB for UE) is k, and then the index of ACK/NACK channel allocated to this UE is also k. Another implicit indication method is to implicitly indicate the index of the ACK/NACK channel allocated to the certain UE according to the index of the radio resource block of the data resource allocated to the UE. For instance, suppose the index of the RB (radio resource block) of the first data allocated by eNodeB for UE is k, then the index of the ACK/NACK channel allocated to this UE is also k.
In the following, the description is focused on the design of the downlink transmission control channel in an LTE system, including the design of paging control channel, the uplink ACK/NACK channel and the downlink/uplink scheduling channel.
According to present discussion in LTE, in the design of the downlink control channel, a channel, which is called the paging channel (PCH), is used to control paging data, mainly transmitting the information on paging group identifier and the paging channel resource indicator. The paging data information is transmitted through the physical resource indicated by the paging control channel. To simplify the design of the downlink control channel, it is supposed in the standardization that the format of the paging control channel is kept the same as that of the downlink L1/L2 control channel, and the very paging channel is operated as a downlink shared channel (DL-SCH) for information transmission.
According to present discussion in LTE, in an LTE system, the uplink non-synchronous random access processing includes four main steps (please refer to FIG. 5 of present patent): at step 501, UE sends an uplink message 1, including a random selected Preamble; at step 502, eNodeB sends a receiving response message “Message 2”, in which eNodeB uses RA-RNTI as a response channel identifier and allocates C-RNTI for the UE. The timing relationship of semi-syn is kept between step 2 and step 1, i.e., UE may wait for one TTI or several to receive “message 2” after it finishes sending “message 1”. The length of the window may be configured semi-statically. The HARQ function is not applied in “message 2”. In “message 2”, responses may be made to several UEs; at step 503, UE sends “message 3”, initiating the RRC connection request. Here, HARQ is applied; at step 504, eNodeB performs RRC contention resolution. Here, HARQ function is also applied.
According to present discussion in LTE, the downlink L1/L2 control channel includes the Downlink Scheduling channel and the Uplink scheduling channel or Uplink grant channel as well as the ACK/NACK channel (which is used to feed back response to the uplink data). In addition, it possibly includes the power control channel (which is used to transmit power control information) and other specific control channels. Since the ACK/NACK channel (which is used to feed back response to uplink data), the power control channel (which is used to transmit power control information) and other specific control channels use fixed or semi-fixed locations in all physical resources to transmit the downlink control information, for the convenience of specifying rules for discussion in present invention, the downlink L1/L2 control channel is specifically referred to channels including Downlink Scheduling channel and Uplink scheduling channel or Uplink grant channel.
The downlink and uplink scheduling channels are used to transmit downlink scheduling signaling and uplink scheduling signaling respectively. In present LTE system, it is supposed that eNodeB transmits the signaling through the former n (n is less than or equal to 3) OFDM symbols in each TTI. The signaling mainly includes UE-ID, the corresponding downlink or uplink physical resource allocation locations and HARQ, MIMO relevant information. In this case, UE-ID is used by the UE to perform UE-ID correlation operation to the received downlink signal so as to determine whether the signal is transmitted to this UE or not, then according to the physical resource indication information in the control signaling, the UE obtains the data channel's physical position and reads out the corresponding data. According to present research progress in LTE, two sequence orders may be used by eNodeB to transmit different UEs' scheduling signaling. As shown in FIG. 6 of present invention, 601, 602, . . . , and 636 represent the corresponding logic numbers of the fundamental control RBs for the transmission of control channel.
In present invention, suppose that the fundamental physical control channel RB is the fundamental physical unit applied to transmit downlink L1/L2 control channel information. It consists of certain number of OFDM sub-carriers which are distributed in time and frequency domain. Then logically sort all fundamental physical control channel RBs that are used to transmit scheduling channels (including all downlink scheduling channels and uplink scheduling channels) to obtain the RBs' logic numbers, i.e., 601, 602, . . . and 636 as shown in FIG. 6. When transmitting scheduling signaling, some criteria should be followed to select the logic number(s) (with this criterion, during the process of selecting the number of the logic numbers, it is necessary to consider MCS value and which specified fundamental physical control channel RBs can be applied in the locations where the scheduling channel can utilize) of either one basic fundamental physical control channel RB or several, then according to the corresponding relation, the corresponding fundamental physical control channel RBs should be obtained for the transmission of control signaling.
According to present research progress in LTE, two methods are proposed for transmitting scheduling information: with the first method, the downlink scheduling signaling of all UEs (that need to transmit scheduling information) is transmitted from the beginning to the end via the locations numbered by the RBs' logic numbers, and the uplink scheduling signaling of all UEs (that need to transmit scheduling information) is transmitted from the very end to beginning via the locations numbered by the RBs' logic numbers. Then following this order, different UEs' downlink or uplink scheduling signaling is transmitted. With the second method, the scheduling signaling is transmitted completely adaptively with no extra constraints on the order of the transmission of uplink or downlink scheduling signaling. The advantage of method one is that it may reduce the number of UE's blind detections, but it would waste some physical resources. No waste of physical resource exists in method two, but the number of UE's blind detections is greater than that of method one.
After analysis to the design of paging control channel in LTE, ACK/NACK channel and uplink/downlink scheduling channel, some disadvantages have been found to present design. Now explanations will be given in the following three aspects:
First, the paging control channel is special compared with the general L1/L2 control channel. However, their property has not been fully considered in present channel design. Through a paging channel, the paging information can be transmitted to one paging group or several and the ID transmitted through the paging control channel is not a certain UE's ID but a Paging Group ID. Therefore, in virtue of matching the Paging Group ID, a UE may determine whether the paging information is for him/her or not. Suppose that eNodeB transmits the paging control channel information through a specific location, UE matches the Paging Group ID with these specific locations to find if there is any paging control channel so that it (who is in Idle Mode) can utilize only detecting process to determine whether there is any paging message for him/her or not. Meanwhile, when it is necessary for this location not to transmit any paging control channel information, it is used to transmit other downlink L1/L2 control channels. In this way, for the UE in Active Mode, it can detect this location after it performs blind detection to other locations where any downlink L1/L2 control channels would be transmitted. In this way, the probability of unnecessary blind detection performed by the UE in Active Mode to the location when this location is used to transmit the paging control channel.
In a second aspect: it is necessary to apply HARQ function in “message 3” in the design of uplink access process. So that it is necessary to design the ACK/NACK channel to confirm whether “message 3” has been correctly received by eNodeB or not. In present LTE system, suppose that this kind of ACK/NACK channel is implicitly bound to the control channel of message 2, i.e., this ACK/NACK channel shares the same downlink channel number as that of the message 2's control channel. However, since message 2 may contain several response messages for UEs, this bind criterion results in that different ACK/NACK channels of different UEs responses to message 3 share the same channel numbers. Therefore, contradictions may come across in different UEs' channel resources. So that it is necessary to find a scheme to settle these contradictions.
In the third aspect: at present, it is necessary for UE to perform several blind detections to the downlink/uplink scheduling channels. So that further optimization may be performed on the design in this aspect.